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From: "H. Peter Anvin" <hpa@zytor.com>
To: Thomas Gleixner <tglx@linutronix.de>,
	Andy Lutomirski <luto@amacapital.net>
Cc: Sebastian Lackner <sebastian@fds-team.de>,
	X86 ML <x86@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	Anish Bhatt <anish@chelsio.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Chuck Ebbert <cebbert.lkml@gmail.com>
Subject: Re: [PATCH 1/2] x86_64,entry: Filter RFLAGS.NT on entry from userspace
Date: Wed, 01 Oct 2014 10:50:35 -0700	[thread overview]
Message-ID: <542C3EEB.8050903@zytor.com> (raw)
In-Reply-To: <alpine.DEB.2.11.1410010119320.4455@nanos>

On 09/30/2014 04:21 PM, Thomas Gleixner wrote:
>>
>> If we ever want those cycles back, I bet that the compat sysenter path
>> could be trimmed down a lot.  For example, I think that all of the
>> zero-extension stuff is unnecessary now that we have the magic syscall
>> wrappers for all (?) syscalls.
> 
> Emphasis on "(?)". So yes, once we verified that ....
> 

I don't think that's true.  Many system calls use exactly the same entry
point for compat and noncompat calls.  I don't see any value in
replicating that code in every system call.

The only time we need to do anything horribly special is when we have an
argument which is a signed long, which fortunately is not at all common.

	-hpa



  reply	other threads:[~2014-10-01 17:51 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-09-30 19:40 [PATCH 0/2] x86_64,entry: Clear NT on entry and speed up switch_to Andy Lutomirski
2014-09-30 19:40 ` [PATCH 1/2] x86_64,entry: Filter RFLAGS.NT on entry from userspace Andy Lutomirski
2014-09-30 21:39   ` Sebastian Lackner
2014-09-30 21:45     ` Andy Lutomirski
2014-09-30 22:23       ` Sebastian Lackner
2014-09-30 22:27       ` Thomas Gleixner
2014-09-30 22:33         ` Andy Lutomirski
2014-09-30 23:21           ` Thomas Gleixner
2014-10-01 17:50             ` H. Peter Anvin [this message]
2014-10-01 17:53               ` H. Peter Anvin
2014-09-30 22:42         ` H. Peter Anvin
2014-10-01  0:27   ` Chuck Ebbert
2014-10-01  0:38     ` Andy Lutomirski
2014-09-30 19:40 ` [PATCH 2/2] x86_64: Don't save flags on context switch Andy Lutomirski
2014-09-30 22:21 ` [PATCH 0/2] x86_64,entry: Clear NT on entry and speed up switch_to Thomas Gleixner
2014-09-30 22:30   ` Andy Lutomirski

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